1. Field of the Invention
The present invention relates to an apparatus for a low pressure chemical vapor deposition, and particularly to an improved apparatus for a low pressure chemical vapor deposition capable of achieving a fabrication of various kinds of thin films having a uniform thickness, preventing breakages of the parts, achieving automation of the system, and combining the use of a low pressure chemical vapor deposition apparatus and a plasma low pressure chemical vapor deposition apparatus.
2. Description of the Conventional Art
As well known to those skilled in the art, the low pressure chemical vapor deposition (hereinafter called an "LPCVD") technique has been widely used so as to deposit nitride layers, oxide layers, silicon layers, and the like on a wafer having insulating, dielectric or conductive characteristics.
The deposition apparatus adopted in the LPCVD is directed to depositing a compound-made thin film on a wafer by reacting a chemical source gas in a reactor under a low pressure. This apparatus includes a single wafer input low pressure chemical vapor deposition device for depositing while loading wafer one by one and a vertical type low pressure chemical vapor deposition device for depositing in a state that a plurality of wafers are loaded. In addition, the single wafer input low pressure chemical vapor deposition apparatus has advantages in that it is easy to make the system automated and does not require wide foot point.
Hereinafter, only the single wafer input low pressure chemical vapor deposition apparatus of the conventional low pressure chemical vapor deposition apparatuses will now be explained.
FIG. 1 shows a conventional single wafer input low pressure chemical vapor deposition apparatus, which includes a deposition base 11 having a wafer inlet 11a and an outlet 1b for discharging reaction substances and opened/closed by an opening/closing plate 11c, a reactor 12 disposed above the deposition base 11 for forming a reaction space "S", a chemical source gas introducer 13 disposed on the upper portion of the reactor 12, and a substrate 14 which is lifted/lowered within the reaction space "S" by a lifting/lowering ram 15 passing through the opening/closing plate 11c.
The above-mentioned conventional single wafer input low pressure chemical vapor deposition apparatus is directed to placing a wafer "W" on the substrate 14 by introducing the wafer "W" through the wafer inlet 11a in a state that the substrate 14 is lowered down to a loading/unloading position lower than the wafer inlet 11a, and lifting the substrate 14 using the lifting/lowering ram 15, driving a substrate heating member 16 disposed at the substrate 14, and introducing chemical source gas into the reactor 12 through a chemical source gas introducer 13, whereby the chemical source gas is deposited on the wafer "W" so as to form a compound thin film.
However, the conventional single wafer input low pressure chemical vapor deposition apparatus has disadvantages in that when heat is applied to the substrate 14 having a wafer "W", since the heat is not applied to the reactor 12 and its periphery, the thermal effect is deteriorated. Due to the above-mentioned thermal effect, the pin hole is caused at the thin film, and the step coverage is decreased.
In addition, because the conventional single wafer input low pressure chemical vapor deposition apparatus provides the chemical source gas introducer 13, connected to a lower portion of the introduction tube 13a passing through the upper surface of the reactor 12, and a shower head 13b having a plurality of shower apertures so as to simply eject chemical source gas, so that a desired compound mixing cannot be achieved, whereby non-uniform layer can be deposited on the entire wafer surface.
Moreover, in order to overcome the above-mentioned problems, the plasma enhanced low pressure chemical vapor deposition apparatus, which is characterized to reacting the chemical source gas by generating plasma by connecting a plasma generator to the substrate and the electrode of the reactor, was introduced.
As shown in FIG. 2, the conventional plasma low pressure chemical vapor deposition apparatus includes a deposition base 21 having an inlet 21a formed at one side thereof and an outlet 21b formed at the other side thereof, wherein the lower portion thereof is opened/closed by an opening/closing plate 21c, a reactor 22 disposed at an upper portion of the deposition base 21, a chemical source gas introducer 23 disposed at the upper surface of the reactor 22, a substrate 24 on which a wafer "W", which can be lifted/lowered within the reactor 22 by a lifting/lowering ram 25 through the opening/closing plate 21c, is mounted, a substrate heating member 26 disposed at the substrate 24, and a plasma generator 27 disposed at the reactor 22 and the substrate 24 and connected to electrodes 27a and 27b.
The above-mentioned conventional plasma low pressure chemical vapor deposition apparatus is directed to depositing a compound thin film on a wafer "W" by lowering the lifting/lowering ram 25 through the opening/closing plate 21c and the substrate 24 down to a loading/unloading position lower than the inlet 21a, by mounting the wafer "W" on the substrate 24 through the inlet 21a, and by generating plasma in the reactor 22 by driving the plasma generator 27 connected to the electrodes 27a and 27b mounted on an upper portion of the reactor 22 and the substrate while introducing the chemical source gas into the reactor 22 through the chemical source gas introducer 23 and while heating the substrate and the wafer "W" by driving the substrate heating member 26 after lifting the substrate 24 with the wafer "W" up to the deposition position.
The above-mentioned plasma low pressure chemical vapor deposition apparatus has advantages in that it can minimize a characteristic variation of a device due to a deposition temperature by maintaining the process temperature at a low temperature by ionizing the chemical source gas by generating plasma. However, it has disadvantages in that the heat effect is deteriorated because the chemical source gas is introduced into a reaction space "S" in a state that the chemical source gas is not substantially heated since only the substrate 24, on which the wafer "W" is mounted, is heated, and its periphery is not substantially heated. In addition, pin hole can occur at the thin film due to the above-mentioned lower heat effect, and the step coverage is deteriorated.
Moreover, because the chemical source gas introducer 23 is simply connected to the introduction tube 23a passing through an upper portion of the reactor 22 and a lower portion of the introduction tube 23a and includes a shower head 23b having a plurality of shower apertures, so that substantial pre-heating and mixing of the introducing chemical source gas are not performed and the wafer "W" which is loaded on the substrate 24 cannot have substantial flooded by the chemical source gas, the uniformity level of the compound thin film is lowered.
In addition, since the wafer "W" mounted on the substrate is directly exposed to the lower portion of the shower head, the wafer "W" is not substantially exposed with respect to the chemical source gas, so that the uniformity level of the thin film is lowered.
Moreover, since the waste gas in the chemical reaction is exhausted from the outlet, and the gas in the reactor cannot be exhausted at a desired speed, the remaining gas affects the quality of the thin film.
Referring to FIGS. 1 and 2, since the conventional low pressure chemical vapor deposition apparatus and the conventional plasma low pressure chemical vapor deposition apparatus provide the substrates 14 and 24 which are connected to an upper portion of the lifting/lowering rams 15 and 25 and lifted/lowered within a range between the loading/unloading position and the deposition position, the desired precise loading/unloading cannot be achieved, disadvantageously affecting automation of the system.
In addition, referring to FIG. 4, the substrates 14 and 24 in the conventional low pressure chemical vapor deposition apparatus and the plasma low pressure chemical vapor deposition apparatus include the wafer placement sections 14b and 24b, on which the wafer "W" is mounted, being higher than the bodies 14a and 24a having the substrate heating member, and wafer supporting protrusions 14c and 24c provided at a periphery of the wafer placement sections 14b and 24b, so that the wafer "W" is stably placed on the wafer placement sections 14b and 24b in the support protrusions 14c and 24c.
However, conventionally, the wafer "W" having a flat zone "F" is circular and is mounted on the substrates 14 and 24 through the wafer inlets 11a and 12a using a robot hand "R". Here, since the fork-shaped robot hand "R" interferes with the wafer placement sections 14b and 24b during a certain operation mode, part of the both inner sides of the wafer placements 14b and 24b are cut away to be straight line sections 14d and 24d, so that the robot hand "R" freely operates between the straight line sections 14d and 24d. In addition, the width between the straight line sections 14d and 24d is smaller than the width between the inner sides of the fork of the robot arm "R".
In the above-mentioned construction, when lowering the robot hand "R" after moving the robot hand "R" to a position precisely mating with the wafer placement sections 14b and 24b, since the robot hand "A" is lowered at the outer side of the straight line sections 14d and 24d of the wafer placement sections 14b, and 24b , there is not any interference between the robot hand "A" and the wafer placement sections 14b and 24b, and the wafer "W" is safely placed on the support protrusions 14c and 24c formed at the rim of the wafer placement sections 14b and 24b. When unloading the wafer, the operation is executed in the reverse order of the above-mentioned order.
However, referring to FIG. 3, when the wafer "W" is placed on the wafer placement sections 14b and 24b, since the both sides of the wafer "W" do not come into precise contact with the wafer placement sections 14b and 24b, that is, the wafer "W" slightly comes off from the straight line sections 14d and 24d of the wafer placement sections 14b and 24b, the heat of the substrate heating member in the substrate bodies 14a and 24a is not evenly transferred to the entire surface of the wafer "W", and a desired deposition cannot be executed with respect to the both sides of the wafer "W", and the deposition with respect to the lower surface of the wafer "W" is executed because the chemical source gas is introduced over part of the lower surface of the wafer "W" in a state that the both sides of the wafer "W" is slightly lifted.
In addition, referring FIGS. 4A and 4B, in order to resolve the above-mentioned problems, wafer lifting/lowering pins 17 and 28 (preferably three) which are lifted/lowered in the wafer placement sections 14b and 24b of the substrates 14 and 24 are provided. That is, as shown FIG. 4A, in a state that the wafer lifting/lowering pins 17 and 28 are lifted, the wafer "W" is positioned on the robot hand "A", and as shown in FIG. 4B, the wafer "W" is stably placed on the wafer placement sections 14b and 24b by lowering the lifting/lowering pins 17 and 28 unless the straight line sections of both sides of the wafer placement sections 14b and 24b formed on the substrate bodies 14a and 24a are not provided.
However, in this case, a certain gap is formed between the substrate bodies 14a and 24a and the wafer lifting/lowering pins 17 and 28 when mounting the wafer lifting/lowering pins 17 and 28. The chemical source gas infiltrates through the gap causing particles. In addition, it is difficult to precisely dispose the substrate heating member and the electrodes in the substrate bodies 14a and 24a. Moreover, the gas infiltrated into the gap affects the substrate heating member causing heat loss. In addition, since the wafer lifting/lowering pins 17 and 28 are made of SUS or quartz, the wafer lifting/lowering pins 17 and 28 can easily broken, and it is difficult to maintain them.